[v2] fs: optimise kiocb_set_rw_flags()
diff mbox series

Message ID 5328b35d948ea2a3aa5df2b1d740c7cb1f38c846.1579224594.git.asml.silence@gmail.com
State New
Headers show
Series
  • [v2] fs: optimise kiocb_set_rw_flags()
Related show

Commit Message

Pavel Begunkov Jan. 17, 2020, 1:32 a.m. UTC
kiocb_set_rw_flags() generates a poor code with several memory writes
and a lot of jumps. Help compilers to optimise it.

Tested with gcc 9.2 on x64-86, and as a result, it its output now is a
plain code without jumps accumulating in a register before a memory
write.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---

v2: check for 0 flags in advance (Matthew Wilcox)

 include/linux/fs.h | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

Comments

Pavel Begunkov Jan. 31, 2020, 1:01 p.m. UTC | #1
On 1/17/2020 4:32 AM, Pavel Begunkov wrote:
> kiocb_set_rw_flags() generates a poor code with several memory writes
> and a lot of jumps. Help compilers to optimise it.
> 
> Tested with gcc 9.2 on x64-86, and as a result, it its output now is a
> plain code without jumps accumulating in a register before a memory
> write.

Humble ping

> 
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
> 
> v2: check for 0 flags in advance (Matthew Wilcox)
> 
>  include/linux/fs.h | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 98e0349adb52..22b46fc8fdfa 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -3402,22 +3402,28 @@ static inline int iocb_flags(struct file *file)
>  
>  static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
>  {
> +	int kiocb_flags = 0;
> +
> +	if (!flags)
> +		return 0;
>  	if (unlikely(flags & ~RWF_SUPPORTED))
>  		return -EOPNOTSUPP;
>  
>  	if (flags & RWF_NOWAIT) {
>  		if (!(ki->ki_filp->f_mode & FMODE_NOWAIT))
>  			return -EOPNOTSUPP;
> -		ki->ki_flags |= IOCB_NOWAIT;
> +		kiocb_flags |= IOCB_NOWAIT;
>  	}
>  	if (flags & RWF_HIPRI)
> -		ki->ki_flags |= IOCB_HIPRI;
> +		kiocb_flags |= IOCB_HIPRI;
>  	if (flags & RWF_DSYNC)
> -		ki->ki_flags |= IOCB_DSYNC;
> +		kiocb_flags |= IOCB_DSYNC;
>  	if (flags & RWF_SYNC)
> -		ki->ki_flags |= (IOCB_DSYNC | IOCB_SYNC);
> +		kiocb_flags |= (IOCB_DSYNC | IOCB_SYNC);
>  	if (flags & RWF_APPEND)
> -		ki->ki_flags |= IOCB_APPEND;
> +		kiocb_flags |= IOCB_APPEND;
> +
> +	ki->ki_flags |= kiocb_flags;
>  	return 0;
>  }
>  
>
Pavel Begunkov Feb. 12, 2020, 12:57 p.m. UTC | #2
On 1/31/2020 4:01 PM, Pavel Begunkov wrote:
> On 1/17/2020 4:32 AM, Pavel Begunkov wrote:
>> kiocb_set_rw_flags() generates a poor code with several memory writes
>> and a lot of jumps. Help compilers to optimise it.
>>
>> Tested with gcc 9.2 on x64-86, and as a result, it its output now is a
>> plain code without jumps accumulating in a register before a memory
>> write.
> 
> Humble ping

Anyone?

> 
>>
>> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
>> ---
>>
>> v2: check for 0 flags in advance (Matthew Wilcox)
>>
>>  include/linux/fs.h | 16 +++++++++++-----
>>  1 file changed, 11 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/linux/fs.h b/include/linux/fs.h
>> index 98e0349adb52..22b46fc8fdfa 100644
>> --- a/include/linux/fs.h
>> +++ b/include/linux/fs.h
>> @@ -3402,22 +3402,28 @@ static inline int iocb_flags(struct file *file)
>>  
>>  static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
>>  {
>> +	int kiocb_flags = 0;
>> +
>> +	if (!flags)
>> +		return 0;
>>  	if (unlikely(flags & ~RWF_SUPPORTED))
>>  		return -EOPNOTSUPP;
>>  
>>  	if (flags & RWF_NOWAIT) {
>>  		if (!(ki->ki_filp->f_mode & FMODE_NOWAIT))
>>  			return -EOPNOTSUPP;
>> -		ki->ki_flags |= IOCB_NOWAIT;
>> +		kiocb_flags |= IOCB_NOWAIT;
>>  	}
>>  	if (flags & RWF_HIPRI)
>> -		ki->ki_flags |= IOCB_HIPRI;
>> +		kiocb_flags |= IOCB_HIPRI;
>>  	if (flags & RWF_DSYNC)
>> -		ki->ki_flags |= IOCB_DSYNC;
>> +		kiocb_flags |= IOCB_DSYNC;
>>  	if (flags & RWF_SYNC)
>> -		ki->ki_flags |= (IOCB_DSYNC | IOCB_SYNC);
>> +		kiocb_flags |= (IOCB_DSYNC | IOCB_SYNC);
>>  	if (flags & RWF_APPEND)
>> -		ki->ki_flags |= IOCB_APPEND;
>> +		kiocb_flags |= IOCB_APPEND;
>> +
>> +	ki->ki_flags |= kiocb_flags;
>>  	return 0;
>>  }
>>  
>>
>

Patch
diff mbox series

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 98e0349adb52..22b46fc8fdfa 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3402,22 +3402,28 @@  static inline int iocb_flags(struct file *file)
 
 static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
 {
+	int kiocb_flags = 0;
+
+	if (!flags)
+		return 0;
 	if (unlikely(flags & ~RWF_SUPPORTED))
 		return -EOPNOTSUPP;
 
 	if (flags & RWF_NOWAIT) {
 		if (!(ki->ki_filp->f_mode & FMODE_NOWAIT))
 			return -EOPNOTSUPP;
-		ki->ki_flags |= IOCB_NOWAIT;
+		kiocb_flags |= IOCB_NOWAIT;
 	}
 	if (flags & RWF_HIPRI)
-		ki->ki_flags |= IOCB_HIPRI;
+		kiocb_flags |= IOCB_HIPRI;
 	if (flags & RWF_DSYNC)
-		ki->ki_flags |= IOCB_DSYNC;
+		kiocb_flags |= IOCB_DSYNC;
 	if (flags & RWF_SYNC)
-		ki->ki_flags |= (IOCB_DSYNC | IOCB_SYNC);
+		kiocb_flags |= (IOCB_DSYNC | IOCB_SYNC);
 	if (flags & RWF_APPEND)
-		ki->ki_flags |= IOCB_APPEND;
+		kiocb_flags |= IOCB_APPEND;
+
+	ki->ki_flags |= kiocb_flags;
 	return 0;
 }